Coccyx

Coccyx
A coccyx with four vertebrae below the sacrum.
Details
Identifiers
Latin	os coccygis
MeSH	A02.835.232.834.229
TA	A02.2.06.001
FMA	20229
Anatomical terms of bone []

The coccyx (/ˈkɒksɪks/ KOK-siks; plural: coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in humans and apes, and certain other mammals such as horses. In animals with bony tails, it is known as tailhead or dock, in bird anatomy as tailfan. It comprises three to five separate or fused coccygeal vertebrae below the sacrum, attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx.

The coccyx is formed of either three, four or five rudimentary vertebrae. It articulates superiorly with the sacrum. In each of the first three segments may be traced a rudimentary body and articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone. The transverse processes are most prominent and noticeable on the first coccygeal segment. All the segments lack pedicles, laminae and spinous processes. The first is the largest; it resembles the lowest sacral vertebra, and often exists as a separate piece; the remaining ones diminish in size from above downward.